The present invention relates to the field of cathode ray tube manufacture, particularly frit knocking. More specifically, the present invention relates to a device and system for heating and maintaining the temperature of a cathode ray tube waiting to undergo a frit knocking process. This is necessary to prevent or minimize arcing during the evaluation of the frit seal in the cathode ray tube using an external high-voltage probe. The present invention provides heated packs that can be applied to the cathode ray tube to increase or maintain its temperature.
Cathode ray tubes (xe2x80x9cCRTsxe2x80x9d) are well known in modern society. The CRT is the principal component in such common devices as television sets and computer and video monitors. As shown in FIG. 1, a CRT (100) typically includes a relatively flat display portion (101) (upper portion as seen in FIG. 1). When one is watching television or looking at a computer monitor, that person is looking at the flat display portion (101) of a cathode ray tube. Below the display portion (101) is a funnel portion (102) that narrows into the xe2x80x9cneckxe2x80x9d of the CRT.
During manufacture, an electro-luminescent material such as phosphorus is coated over the display portion (101) of the CRT. The display portion (101) is then joined to the funnel (102) using a glass paste compound known as frit. A bead of frit is distributed around the interface between the funnel (102) and the display portion (101). The frit is the cured or hardened to form an airtight seal between the display portion (101) and the funnel (102). This seal may be referred to as a frit seal (103).
An electron gun (not shown) is then placed at the end of the CRT""s xe2x80x9cneckxe2x80x9d (102). When the CRT is operated, a yoke (not shown) creates an electromagnetic field and causes the stream of electrons emitted from the electron gun to scan in lines across the surface of the display portion (101). Where the stream of electrons hits the electro-luminescent material, the electro-luminescent material emits light. Thus, by rapidly switching the electron stream on and off, or by varying the power of the electron stream as it sweeps across the display portion of the CRT, an image can be formed in the light emitted by the electro-luminescent material. This is the general principle on which CRTs operate.
After the display portion (101) of the tube is joined to the funnel (102) and the joint between the two is sealed with frit, the completed tube is evacuated. Then, the strength of the frit seal (103) and the integrity of the vacuum are evaluated. This evaluation is known as xe2x80x9cfrit knockingxe2x80x9d and is performed by applying a high-voltage to the anode or funnel portion (102) of the CRT.
In the frit knocking process, a conductive band or strap (104) is wrapped around the frit seal (103) and is in physical and electrical contact with the frit seal (103). The conductive band (104) is grounded (105) as shown in FIG. 1. A high-voltage probe (106) is then positioned to apply a voltage to the anode of the CRT. The probe (106) is connected to a voltage source (109) that provides a high voltage output. The tip (107) of the probe is then brought into contact with a point (108) on the anode or funnel portion (102) of the CRT (100).
If there is any flaw in the frit seal (103), such as an opening, a fracture, a gap, etc., the high-voltage probe (106) will create an electrical arc from within the CRT (100), through the flaw in the frit seal (103) and into the grounded band (104). If such arcing is detected, the failure or lack of integrity in the frit seal (103) is also detected. If such arcing is detected, the CRT (100) must be removed from the production line so that the frit seal (103) can be repaired, patched or replaced. Otherwise, the flaw in the existing frit seal may degrade or even disable the performance of the CRT (100).
While this method provides an adequate means of testing or xe2x80x9cknockingxe2x80x9d the frit seal in a cathode ray tube, there are also significant problems. Specifically, the distance (d) between the tip (107) of the high-voltage probe (106) and the grounded band (104) is small enough that electrical arcing (130) may occur outside the CRT (100) between the probe tip (107) and the grounded band (104).
This arcing (130) poses many problems. For example, the arcing (130) may be detected and attributed to a flaw in the frit seal (103). If this error is not detected, the CRT (100) will not pass the evaluation even though its frit seal (103) may be in perfect condition. Additionally, even if the error is detected, time may be required to reset the testing apparatus that is erroneously registering a flaw in the frit seal (103). External arcing (130) may also damage the equipment being used to evaluate the frit seal (103).
A critical factor that contributes to this external arcing (130) is the temperature of the cathode ray tube. During normal processing in the CRT production line, the CRTs are maintained at an elevated temperature which minimizes the possibility of external arcing during frit knocking.
However, it sometimes happens production is interrupted or, for some other reason, a tube or tubes must be removed from the production line before frit knocking is performed. When these tubes are ready to be reintroduced to the production line and have their frit seals evaluated, the tubes may have cooled. The cooled tubes are much more likely to experience unwanted external arcing during the frit knocking.
Consequently, there is a need in the art for a method and system of heating or maintaining the temperature of cathode ray tubes that have been temporarily pulled from a production process just prior to frit knocking.
The present invention meets the above-described needs and others. Specifically, the present invention provides a method and system of heating or maintaining the temperature of cathode ray tubes that have been temporarily pulled from a production process just prior to frit knocking.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.
The present invention may be embodied and described as a system for heating or maintaining the temperature of a cathode ray tube that is waiting to undergo a frit knocking process. The system preferably includes a heat pack for transferring heat to the cathode ray tube; and an oven for heating the heat pack. A cord is connected to the heat pack by which the heat pack can be suspended on, and in thermal contact with, the cathode ray tube. Preferably, the heat pack is a flexible bag with a heat-retaining and transmitting material disposed in the bag.
Preferably, the oven includes a control system. The control system may include both a thermostat for monitoring the temperature of the oven and a timer for controlling the oven or monitoring the amount of time heat packs have been heated.
The system of the present invention may also include a thermally-insulating envelope sized to receive the cathode ray tube. This envelope may be used to help the cathode ray tube hold its heat, with or without using a heat pack to heat the tube.
The present invention also encompasses the methods of making and using the system described above. However, the method of the present invention is broader than the use of the heat packs described above. The present invention includes a method of preventing external arcing during a frit knocking process in a cathode ray tube production line by heating a cathode ray tube which is waiting to undergo frit knocking. This method may be performed by heating a heat pack; and applying the heated heat pack to the cathode ray tube, such that the heat pack transfers heat to the cathode ray tube.